1. For diagnosis: (1) Differentiation of non-infectious arthritis. From the observed pathological changes such as congestion and edema of the synovial membrane, the degree of cartilage damage and the presence or absence of crystalline material in the joint, it can assist in differentiating rheumatoid arthritis, osteoarthrosis and crystalline arthritis. (2) To understand the site, degree and morphology of meniscal injury of the knee joint. (3) Injury to the cruciate ligament and N tendon stop of the knee joint. (4) To understand the intra-articular cartilage damage, the presence of intra-articular free bodies, etc., in order to confirm the diagnosis of osteoarthrosis, especially long-term chondromalacia of the patella. (5) Analyze the etiology of chronic synovitis, such as pigmented villous nodular synovitis. (6) Diagnosis of synovial crease syndrome and fat pad lesions of the knee, (7) Site and extent of rotator cuff rupture and biceps tendon adhesions. (8) Synovial biopsy. 2.For the study of changes in intra-articular lesions: During the development of joint diseases, arthroscopy can be performed several times. By taking pictures, videos or synovial biopsies, information that is difficult to obtain by other diagnostic methods can be obtained, which is extremely helpful for diagnosis, treatment and prognosis. 3.For treatment: For some lesions of the knee and shoulder joints, after a clear diagnosis of the researcher, surgery can be performed with special instruments under microscopic view, and satisfactory results can be achieved. For example, joint irrigation and debridement, partial or complete excision of torn meniscus of knee joint, suture of meniscus edge, anterior cruciate ligament repair, synovial crease excision, intra-articular adhesion release, tibial plateau or intercondylar crest fracture repair, rotator cuff debridement, biceps tendon adhesion release and intra-articular free body removal, etc. In addition, major synovectomy is feasible for rheumatoid arthritis disease of the large joints of the extremities. The only absolute contraindication is joint stiffness, as it prevents arthroscopic manipulation. For those who have had a recent arthrography, due to the possibility of secondary chemical synovitis. False positive results can be obtained if the arthroscopy is performed within 1 week after the imaging. In patients with bleeding disorders, although intraoperative bleeding can be flushed with a large amount of saline to obtain a good field of view for diagnosis, a large amount of joint hemorrhage can occur after surgery. These two points should be paid special attention when choosing arthroscopy.